Add epic option while creating a new issue in UI

Since we'll be adding the ability to ad issues directly from the epic page, it makes sense to add the Epic field here too:

Proposal

Add Epic option, under Assignee
User can add an Epic similarly to how they would add an epic from the sidebar
Push items "down" the list, therefor weight is now in the next column above due date

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Edited Nov 08, 2021 by 🤖 GitLab Bot 🤖